1. Field of the Invention
The present invention relates to a mold for molding a plastic, more particularly to a mold for injection molding of a plastic by means of which undercut portions can be formed at both sides of a partition wall of an injection-molding product.
2. Description of the Prior Art
Injection molding is one method for molding a plastic wherein a melted plastic is injected into a cavity of a mold having a predetermined shape, and then is cooled so as to be solidified thereby forming a product having a shape identical to a shape of the cavity.
Generally, such mold comprises a fixing plate and a moving plate which is detachably coupled to the fixing plate. When the moving plate is coupled to the fixing plate, the cavity is formed therebetween. If an injection-molding product has an undercut portion which interrupts the moving plate from moving in the forward or backward direction with respect to the fixing plate thereby preventing the injection-molding product from being ejected from the cavity, an auxiliary member such as a molding pin or a stripper is required for ejecting the injection-molding product from the cavity.
FIG. 1a shows a conventional mold for molding a plastic which is used for making a ledge which is installed at a freezing chamber of a refrigerator and on which an ice vessel is mounted.
As shown in the figure, the mold comprises a fixing plate 10, a moving plate 20, an eject plate 30 and a plurality of molding pins 40.
Moving plate 20 can move in the forward or backward direction with respect to fixing plate 10 such that moving plate 20 can be coupled to or separated from fixing plate 10. Moving plate 20 includes a front plate 24 and a rear plate 26 which is spaced by a predetermined distance apart from front plate 24 by means of connecting rod 28.
Fixing plate 10 has a fixing core 12 and moving plate 20 has a moving core 22 which faces to fixing core 12. Fixing core 12 is incorporated with moving core 22 so as to form a cavity in which a product 50 is molded.
Eject plate 30 is provided between front plate 24 and rear plate 26 of moving plate 20 such that eject plate 30 can be moved in the forward and backward directions along connecting rod 28 which connects front plate 24 and rear plate 26 to each other.
In addition, the plurality of molding pins 40 have prominence-depression portions 42 for forming undercut portions to product 50. Molding pins 40 obliquely pass through moving core 22 and end portions thereof are coupled to eject plate 30 in such a manner that molding pins 40 slidably move along eject plate 30 within a predetermined range.
In the above construction as shown in FIG. 1a, in a state when the mold is closed, a melted plastic is injected into the cavity formed between fixing and moving cores 12 and 22 through a gate (not shown), so ledge 50 for mounting the ice vessel is formed in correspondence to the shape of the cavity.
When the molding of ledge 50 has been finished, as shown in FIG. 1b, moving plate 20 including moving core 22, eject plate 30 and molding pins 40 are withdrawn from fixing plate 10 together with molded ledge 50 for mounting the ice vessel, so the mold is opened.
After that, eject plate 30 is again moved toward fixing plate 10 so that molding pins 40 coupled to eject plate 30 are moved toward fixing plate 10 thereby separating the product, that is ledge 50, from moving core 22.
At this time, since molding pins 40 obliquely pass through moving plate 20 having moving core 22, molding pins 40 are slid in the lateral direction while they are moving in the forward direction. Accordingly, prominence-depression portions 42 of molding pins 40 are separated from the undercut portions of ledge 50 so that the ejection of ledge 50 is possible. FIG. 1c shows ledge 50 separated from prominence-depression portions 42 of molding pins 40.
However, the conventional mold used in the injection molding of the plastic cannot make undercut portions at both sides of a partition wall of the injection-molding product. In other words, there is required a predetermined distance between the prominence-depression portions of the molding pins in order to prevent two molding pins moving in the opposite directions to each other along the eject plate from interfering with each other. That is, the conventional mold does not make the undercut portions to both sides of one guide rail so as to allow two ice vessels to share a guide rail 52 of ledge 50 as shown in FIG. 1a. Accordingly, there is required two partition walls having a predetermined distance therebetween in order to provide a partition section having the undercut portions at both sides thereof. As a result, materials are unnecessarily wasted, so that not only is manufacturing cost increased, but also the design of the product is limited.